This application claims benefit of Japanese Patent Application No. 2002-080707 filed on Mar. 22, 2002, the contents of which are incorporated by the reference.
The present invention relates to voice data transmitting and receiving systems and, more particularly, to voice data transmitting and receiving systems with improved voice quality in voice communication via internet or like non-QoS (quality of service) guaranteed network.
As for internet communication now commonly utilized perfectly beyond country borderlines all over the world, electronic market transactions and internet telephone communication (such as IP telephone communication and internet protocol telephone communication) have been attracting attentions aside from the conventional applications such as home page reading, electronic mails and file transfer. This is greatly attributed to by quick development of networks centered on line switching in telephone network but also IP networks based on packet switching.
In the IP telephone communication, various data including voice (or FAX) data (such as still images and motion picture images) are converted to IP packets for transfer thereof in IP base network. A voice telephone services partly or fully utilizing IP network techniques is referred to IP telephone. Among the IP telephones, the voice telephone service utilizing e the same IP network as those in www therein (i.e., communication network for communication with internet protocol), is referred to as internet telephone communication.
As for the IP telephone communication, there are the following three systems. In a first system, in which voice messages are exchanged between dial-up connected personal computers, both personal computers have to install the same software to this end and be connected to the server. In a second system, in which a telephone call is made from a personal computer to a general subscriber telephone set (not vice versa), no communication can be obtained unless both sides make promises beforehand. As a third communication, in which communication is made between general subscriber telephone sets, are a system, in which communication is made by inputting user ID and PIN to the juncture between internet network in public telephone line switching system via a gateway for internet telephone, and a system for communication with direct internet-coupled terminals. These third systems are closest to the present telephone communication system, and their technical advancement is pronounced.
By the way, in voice communication in IP via an IP network such as a non-QoS (quality of service) guaranteed internet or a local network, usually voice data using RTP of UDP protocol are usually transmitted and received. In this case, voice communication and motion picture reproduction are made by using RTP with importance attached to the real time property of the data. However, the RTP has no measure against packet losses generated in the communication channel, and packets loses in the channel are no longer transmitted again, thus leading to the problems in the voice quality such as interruption of voice.
To cope with these problems, a system is proposed, in which, lest voice should be interrupted irrespective of packet losses, the data transmission is performed by adding immediately preceding and immediately succeeding packet data for execution of an interpolation process based on these data. However, in a situation that data communication other than voice is frequently brought about, voice packet losses are pronounced, and in an extreme case the voice quality is deteriorated so greatly that no conversation is obtainable even by using the interpolation.